[Pollinator] Are we underestimating the decline in B. affinis?

[Droege, Sam]

So, friends... in newspaper accounts, in almost everyone single one, we see
the statement that *B. affinis* populations have declined by 87%.

But have they?  I think this is an inaccurate presentation of the situation
and a misinterpretation of the FWS assessment of population status:

See:
https://www.fws.gov/midwest/endangered/insects/rpbb/pdf/SSAReportRPBB.pdf

In fact, I think this values greatly under-represents declines in this
species.

First in the FWS report they talk about an 89% decline in the number of
U.S. counties occupied, it does not mention 87% anywhere, so am not sure
where that figure came from.

That 87/89% figure does not seem to account for any Canadian counties (or
whatever the comparable jurisdiction might be).

These figures also define occupancy data for a county as a specimen of *B.
affinis *collected after 2000 as "occupied" but is that the best value?
>From Ohio East there have been thousands and thousands of bumble bees
collected and photographed and only a handful of specimens of *B. affinis *have
been collected.  In most of these "occupied" counties only single
individuals were collected.

Bees collected in the early 2000's and not seen since are almost certainly
the tail end residue of formerly healthy populations, not representatives
of hidden *B. affinis *populations, or people would have found more
afterwards ...like they have in the Upper Midwest.

An occupied county should have locations where *B. affinis *can be found
every year, again this is what we see in some places in the Upper Midwest
but do not see outside that area.

Note too that the number of counties occupied is a very different thing
from population size.

1 single bumble bee or 100,000 bumble bees in an individual county both
yield a value of "occupied" for that county but the actual population size
would be orders of magnitude different.

Currently I know of no active colonies of *B. affinis *from Ohio East

If we use the more conservative designation (and I think more accurate) of
an occupied county as a county having regularly occurring *B. affinis *in
the last 5 years then we have to presume that *B. affinis* lack viable
populations from Ohio East.

In the Upper Midwest and perhaps Southern Ontario, there are extant
colonies of *B. affinis*  But are the number of bees in those counties at
their historic highs?  Likely not.  We don't even have accurate information
about the trends or status in these residual sites, but all arrows point
towards these as small not large populations.

I think we need to better clarify the values going out to the public
regarding populations status and put the proper perspective on this matter.


Biologically, population size has almost certainly declined far more than
99.9%.  And if you defined occupancy at a smaller geographic scale than a
county then occupancy decline is also probably near 99.9%.

I think we have to stop using the value of 87%...particularly when it gets
transmitted or interpreted as population decline rather than a perhapsa
 too rosy estimation of occupancy.

sam

Sam Droege  sdroege at usgs.gov
w 301-497-5840 h 301-390-7759 fax 301-497-5624
USGS Patuxent Wildlife Research Center
BARC-EAST, BLDG 308, RM 124 10300 Balt. Ave., Beltsville, MD  20705
Http://www.pwrc.usgs.gov

"Statistics should be like a drunk leaning on a lamppost; for
support rather than illumination."
     -author unknown

-- 
*Bees are Not Optional*

*Apes sunt et non liberum*
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